Molding resin composition and method of molding

ABSTRACT

The present invention provides a resin composition suitable for molding a microscopic structure that has small cure shrinkage, good mold transfer properties and excellent properties for post-processing such as polishing processing and laser processing. Such a resin is a thermosetting resin composition comprising 95 to 35 wt % of a thermosetting resin and 5 to 65 wt % of organic filler having a particle size of 10 μm or less. From such a resin, an ink ejecting apparatus having a microscopic structure, for example, a nozzle of a diameter of 30 μm, is integrally molded.

TECHNICAL FIELD

The present invention relates to a resin composition suitable formolding, for example, a liquid ejecting apparatus having a precise andmicroscopic structure, such as a micro-pump, a micropipetter or aninkjet head.

BACKGROUND ART

As research on medical and biochemical research fields, especially genetherapy or genetic engineering, has made progress, mixing a very smallamount of reagents has been increasingly required. Therefore, dispensingmethods are required to be shifted from conventional syringe methods tomethods in which a very small amount of droplets can be dispensed.

Furthermore, in the field of inkjet printers, there is a demand for highquality and high speed printing, so that the need for highly integratedinkjet heads having a narrow nozzle pitch has increased. Therefore,various droplet ejecting apparatuses having a micro-channel structure towhich a micromachining technique such as LIGA process, etching andmicro-pressing is applied have been devised and put to practice.

A molding resin material used for producing such an apparatus isrequired to have small shrinkage so that near-net-shape processing ispossible, have flowability that allows molding a precise microscopicstructure, and have chemical resistance.

However, at present, resins commonly used as molding resin material arethermoplastic resins, which have a large thermal expansion coefficientso that after injection forming, shrinkage occurs in the mold, andnear-net-shape forming is not achieved. Therefore, in order to obtain adesired thermal expansion coefficient or shrinkage ratio, a method ofadding inorganic fillers such as glass fibers to the resin was examined.However, when a resin composition containing inorganic fillers is usedto mold a precision component, the precision component cannot beprocessed uniformly after the molding. In other words, since thehardness of the resin, which is the main component, is very differentfrom that of the glass fibers which are the inorganic fillers, roughnesstends to occur at the time of polishing. Furthermore, the maximumabsorption wavelength of laser light of the resin is very different fromthat of the glass fibers, so that some portions are unprocessed duringlaser processing, and therefore precise finishing cannot be achieved.

Therefore, there is a need for a resin composition suitable for moldingmicroscopic structures. That is, there is a need for a resin compositionfor molding having small shrinkage ratio, good mold transfer propertiesand excellent properties for post-processing such as polishingprocessing or laser processing.

DISCLOSURE OF INVENTION

The inventors of the present invention conducted research to solve theabove-described problems and found that a desired resin compositionsuitable for molding a microscopic structure can be obtained by mixing aspecific amount of an organic filler having a specific particle size toa thermosetting resin and thus achieved the present invention.

The present invention provides a thermosetting resin compositioncomprising 95 to 35 percent by weight (wt %) of a thermosetting resinand 5 to 65 wt % of an organic filler having a particle size of 10 μm orless.

In one preferable embodiment, the thermosetting resin is selected fromthe group consisting of epoxy resin, phenol resin, polyester resin,polyimide resin, urea resin, melamine resin and guanamine resin.

In another preferable embodiment, the organic filler is a spherical orirregular shaped powder selected from the group consisting ofunsaturated polyester, phenol resin, guanamine resin, melamine resin,polyetheretherketone, polysulfone, polyethersulfone and polyimide resin.

The present invention can provide a molding resin having small cureshrinkage, good mold transfer properties and excellent properties forpost-processing such as polishing processing or laser processing.

Furthermore, the present invention provides a method for producing amolded structure having a microscopic structure comprising introducingany one of the above-described thermosetting resin compositions to amold, and heating the mold.

Furthermore, the present invention provides a method for producing amolded structure having a microscopic structure by integral moldingthree-dimensionally with the same resin, the method comprising:introducing the above-described thermosetting resin composition to amold; heating the mold; and molding the obtained molded articleintegrally with another molded article that was molded with a differentmold.

Furthermore, the present invention provides a molded structure having amicroscopic structure obtained by integrally molding any one of theabove-described thermosetting resin compositions.

In one preferable embodiment, the molded structure is an ink ejectingapparatus.

Furthermore, the present invention provides a method for producing anink ejecting apparatus comprising: introducing the thermosetting resincomposition to a mold of a nozzle chamber plate; heating the mold so asto mold a nozzle chamber plate in which a nozzle having a hole size of500 μm or less can be formed; molding a vibration plate with thethermosetting resin composition; and molding integrally the obtainednozzle chamber plate and the obtained vibration plate.

In one preferable embodiment, the method includes forming nozzle holesof the nozzle chamber plate and then molding integrally with thevibration plate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an ink ejecting apparatus when viewedfrom the side of the lower surface.

FIG. 2 is a cross-sectional view of a mold for molding a nozzle chamberplate.

FIG. 3 is a view that shows a curing after molding.

FIG. 4 is a view showing excimer laser processing of a conventionalmolded article containing glass fibers.

FIG. 5 is a view showing excimer laser processing of the molded articleof the present invention.

FIG. 6 is a graph showing the relationship between the wavelength andthe absorbance of each material.

FIG. 7 is a view showing a method for applying varnish.

FIG. 8 is a view showing a method for joining a vibration plate and anozzle chamber plate.

BEST MODE FOR CARRYING OUT THE INVENTION

A thermosetting resin used in the present invention can be any resin, aslong as it can be cured by heat. Examples thereof include, but are notlimited to, epoxy resin, phenol resin, polyester resin, and polyimideresin. Epoxy resin is preferable.

There is no particular limitation regarding the organic filler used inthe present invention. Any organic filler can be used, as long as it isnot melted at a temperature at which a thermosetting resin is cured.Preferably, unsaturated polyester, phenol resin, guanamine resin,melamine resin, polyetheretherketone, polysulfone, polyethersulfone, andpolyimide resin can be used. Guanamine resin is preferable.

The organic filler is added for the purpose of adjusting the viscosityand/or the linear expansion coefficient of a thermosetting resincomposition to reduce cure shrinkage or adjusting the absorbance oflaser light, and serves as aggregate when molding. In order to achievethese purposes, it is preferable that the organic filler is in the formof spherical particles or irregular shaped powder having a size of 10 μmor less. In the case of irregular shaped powder, the largest diametercan be 10 μm or less. When it exceeds 10 μm, it tends to be difficult toadjust the viscosity or the linear expansion coefficient of thethermosetting resin. A preferable particle size is generally 0.5 to 10μm, and more preferably 1 to 5 μm, but the particle size can bedetermined in view of the viscosity and the linear expansioncoefficient, depending on the microscopic structure to be molded.

When using an epoxy resin as the thermosetting resin and a guanamineresin as the organic filler, the thermal expansion coefficient of thecomposition is 2 to 7×10⁻⁵, preferably 5 to 6×10⁻⁵, and the cureshrinkage ratio is preferably 0.8% or less.

The organic filler is contained at 5 to 65 wt % in the thermosettingresin composition. When it is less than 5 wt %, the function as theaggregate is deteriorated, which may cause a problem regarding thestrength of a molded article and may cause curvature or deformation.When it exceeds 65 wt %, the flowability of the resin composition isdeteriorated, which makes it difficult to fill the resin compositioninto a fine portion of a mold.

The thermosetting resin composition of the present invention may containa component used by those skilled in the art such as a releasing agentin a range that does not inhibit the purpose or the advantages of thepresent invention.

The thermosetting resin composition of the present invention can be usedfor producing general resin molded articles, but in particular, it canbe used preferably in the field of precision molding such as integralmolding of a molded structure having a microscopic structure.

Examples of the molded structure having a microscopic structure referredto in the present invention include various precision apparatuses in themicromachining field. For example, an ink ejecting apparatus for aninkjet printer, which is best known as a droplet ejecting apparatus, anapparatus for ejecting a very small amount of droplets or the like areincluded.

“Microscopic structure” refers to a structure of several microns to 500μm, for example, a pin structure, a nozzle, or a gap. “Micro-opening”refers to an opening (regardless of the shape) having a size of about 10to 200 μm, preferably about 30 to 100 μm.

Hereinafter, a molded structure having a micro-opening and production ofthe molded structure by three-dimensionally integral molding will bedescribed by taking molding of an ink ejecting apparatus for an inkjetprinter (which may be referred to simply as “ejecting apparatus” in thefollowing) as an example.

First, an outline for producing an ink ejecting apparatus of the presentinvention will be described. The method includes the steps of:introducing a thermosetting resin composition to a mold of a nozzlechamber plate; heating the mold so as to mold a nozzle chamber plate inwhich a nozzle having a hole size of 500 μm or less can be formed;molding a vibration plate with a thermosetting resin composition(preferably the same resin composition); and integrally molding theobtained nozzle chamber plate and the vibration plate.

The nozzle chamber plate and the vibration plate can be formed one afteranother regardless of the order, or can be formed at the same time. Thenozzle holes of the nozzle chamber plate can be formed before beingmolded integrally with the vibration plate, or can be formed after theintegral molding, but preferably before the integral molding.

Hereinafter, the method will be described with reference to theaccompanying drawings. FIG. 1 is a perspective view of an ejectingapparatus 1 when viewed from the side of the lower surface. In theejecting apparatus 1, a nozzle chamber plate 2 and a vibration plate 3on the nozzle chamber plate 2 are arranged, and thus a discrete inkcompartment 4, a discrete ink channel 5, and a common ink channel 6 aredefined. Nozzles 7 are provided on the lower surface of the nozzlechamber plate 2, corresponding to each discrete ink chamber 4. Thenozzles 7 generally have a size of 30 to 100 μm.

In order to produce such a nozzle chamber plate 2, for example, a moldas shown in FIG. 2 is used. The mold shown in FIG. 2( a) includes anupper mold 10, a lower mold 11 and a molding piece 12. The molding piece12 includes a number of pins with 30 to 100 μm diameter constituting thenozzles 7 of the nozzle chamber plate 2. FIG. 2( b) is an enlarged viewof the vicinity of the boundary of the molding piece 12 and the lowermold 11. The pins 14 of the molding piece 12 are spaced away from theupper surface 15 of the lower mold 11 by a gap 18. This gap is formed inorder to prevent the pins 14 from being bent or damaged by coming intocontact with the upper surface 15 of the lower mold 11. It is preferablethat this gap 18 is 1 to 100 μm.

The molding piece 12 is produced so as to have fine pins by using a LIGAprocess, discharge processing, cutting processing or a combinationthereof.

The thermosetting resin composition is injected into a space 13 definedby the upper mold 10, the lower mold 11 and the molding piece 12 and isheated so that the thermosetting resin is cured and the chamber plate 2provided with the nozzles 7 closed by a thin film(plate) is molded. Itis preferable that the gap 18 is smaller than the particle size of theorganic filler 16. This is because the organic filler prevents orreduces the penetration of the thermosetting resin 17 from the gap 18,and therefore the post-processes for letting the nozzles 7 appear (e.g.,polishing processing and laser processing) can be performed easily.

FIG. 3 shows that the nozzle chamber plate 2 is placed in a cassette 21for curing in order to obtain a smooth surface of the nozzle chamberplate 2 and stabilize the texture. Curing is performed at an appropriatetemperature (e.g., 150 to 200° C.) for an appropriate time (3 to 8hours) while heating.

After the curing, the nozzle chamber plate 2 is subjected to a polishingtreatment or laser processing, so that a nozzle chamber plate 2 havingopen nozzles can be obtained.

FIG. 4 is a schematic view showing the results of subjecting aconventional resin containing glass fibers to an excimer lasertreatment. The resin is melted by the excimer laser treatment and thenozzles 7 are formed. However, glass fibers 22 remain in the channel andinhibit liquid flow. On the other hand, as shown in FIG. 5, in a moldedarticle obtained by the present invention, nozzles 7 having a smoothsurface are formed, and the resin does not remain. The reason for thisseems to be as follows. As shown in FIG. 6, the absorbance at a certainwavelength of the epoxy resin is very different from that of the glassfibers. Therefore, the glass fibers cannot be melted. On the other hand,as shown in an example where a guanamine resin is used as the organicfiller, since the wavelength for maximum absorption of the epoxy resinis very close to that of the guanamine resin, both the epoxy resin andthe guanamine resin can be melted by a laser light. Furthermore, sincethe resin to be removed in the fine opening portion obtained by thepresent invention is very thin as described, it can be removedefficiently.

The obtained nozzle chamber plate 2 is subjected to a surface treatmentwith a plasma asher in order to increase the wettability of the channeland bonding ability to the vibration plate.

On the other hand, the vibration plate 3 molded with the samethermosetting resin composition in the same manner as for the nozzlechamber plate 2 is placed on a stage 23, as shown in FIG. 7. Then, whilethe stage is rotated at an appropriate number of rotations per minute,for example, 1000 to 2000 rpm, a few drops of the varnish 24 having thesame components as those of the chamber plate 2 (e.g., phenolicnovolak-type epoxy resin) are applied, and then a solvent is evaporatedat an appropriate temperature (e.g., 60° C. to 80° C.) and dried.Therefore, as shown in FIG. 8, reference pins 26 are passed throughreference holes 25 of the vibration plate 3 and the nozzle chamber plate2, and they are placed in a cassette 30 and bonded at an appropriatetemperature (e.g., 150 to 180° C.) for appropriate time (e.g., 10 to 30minutes) for curing.

Positioning before the joining can be performed with transmitted light.Alternatively, spot joining can be performed with an iron having aheated head for temporary bonding.

In this manner, the three-dimensionally integrally molded ink ejectingapparatus 1 comprising the nozzles 7, the discrete ink chamber 4, thediscrete ink channel 5 and the common ink channel 6 can be obtained.

Furthermore, if a method for joining molded articles by bonding insidethe mold is used, various kinds of precision equipment in themicromachining field such as an ink ejecting apparatus can be producedeasily and inexpensively.

In the above description, the parenthesized temperatures, time and thelike are examples for the case where an epoxy resin is used as thethermosetting resin and a guanamine resin is used as the organic fillerparticles.

EXAMPLE

Hereinafter, the present invention will be described by way of example,but the present invention is not limited by this example.

Production of Nozzle Chamber Plate

Epicron N770 (manufactured by Dainippon Ink & Chemical Inc.), a phenolictype curing agent TD2106 (manufactured by Dainippon Ink & Chemical Inc.)and a curing accelerator of an imidazole based compound were mixed for areaction, and thus a phenolic novolak type epoxy resin was obtained.Then, 40 wt % of the phenolic novolak type epoxy resin, 57 wt % of aguanamine resin (benzoguanamine resin Epostar M30 manufactured by NipponCatalyst K.K.) having a particle size of 3 μm, and 3 wt % of metallicsoap of a stearate serving as a releasing agent were mixed so as toprepare a thermosetting resin composition. The thermal expansioncoefficient of this resin composition was 6×10⁻⁵, and the cure shrinkageratio was 0.78%. A mixture obtained by adding 57 wt % of glass fibersinstead of the guanamine resin was used as a comparative example. Theresin composition of this comparative example was oriented, the thermalexpansion coefficient was 2 to 5×10⁻⁵, and the cure shrinkage ratio was0.2 to 0.5%. The thermal expansion coefficient and the linear expansioncoefficient was measured by a thermomechanical analysis (TMA) method,and the cure shrinkage ratio was measured according to the method of JISK 6911.

The obtained thermosetting resin composition was injected into a moldhaving the molding piece shown in FIG. 2 and heated to 180° C. At thispoint, pins having a diameter of 30 μm were formed in the molding piece.Furthermore, since the gap 18 shown in FIG. 2 is 2 μm or less which ussmaller that the organic filler particle, a nozzle chamber plate havinga thin plate in the nozzle portion was obtained. This nozzle chamberplate was placed in the cassette shown in FIG. 3, and curing wasperformed at 180° C. for 6 hours. Then, an excimer laser processing wasperformed to add a channel, and thus a nozzle chamber plate includingnozzles having a diameter of 30 μm was obtained.

On the other hand, in the nozzle chamber plate of the comparativeexample, it was confirmed by a scanning electron microscope (SEM) thatthe glass fibers remained in the channel.

(Ink Ejecting Apparatus for an Inkjet Printer)

A vibration plate (thickness of 300 μm) having the same size as thechamber plate was made with the same resin composition as above. Thevibration plate was placed on a stage, and three varnish drops weredropped and applied thereon while the stage was rotated at 1200 rpm, andthen dried at 80° C.

Then, the obtained chamber plate and the vibration plate were bonded atthe reference pins while aligning the reference holes, as shown in FIG.8, and placed in a cassette and bonded at 180° C. for 20 minutes. Thus,an integrally molded ink ejecting apparatus for an inkjet printer wasobtained. When this ink ejecting apparatus was mounted in an inkjetprinter and examined, it was confirmed that uniform and clear printedletters without blur were obtained.

INDUSTRIAL APPLICABILITY

The thermosetting resin composition of the present invention can providea molded article having a precise and complex structure that could notbe obtained by a conventional injection molding by employing a specificrange of an inorganic filler having a specific particle size. Inparticular, an ink ejecting apparatus for an inkjet printer includingnozzles having a diameter of about 30 μm can be integrally moldedeasily.

1. A method for producing an ink ejecting apparatus comprising:introducing a thermosetting resin composition comprising 95 to 35 wt %of a thermosetting resin and 5 to 65 wt % of an organic filler having aparticle size of 10 μm or less and having a thermal expansioncoefficient of 2 to 7×10⁻⁵ and a solidification contraction ratio of0.8% or less to a mold of a nozzle chamber plate; heating the mold so asto mold a nozzle chamber plate in which a nozzle having a hole size of500 μm or less can be formed; molding a vibration plate with athermosetting resin composition comprising 95 to 35 wt % of athermosetting resin and 5 to 65 wt % of an organic filler having aparticle size of 10 μm or less and having a thermal expansioncoefficient of 2 to 7×10⁻⁵ and a solidification contraction ratio of0.8% or less; and molding integrally the obtained nozzle chamber plateand the obtained vibration plate, to form the inkjet ejecting apparatus.2. The method according to claim 1, wherein the thermosetting resin isselected from the group consisting of epoxy resin, phenol resin,polyester resin, polyimide resin, urea resin, melamine resin andguanamine resin.
 3. The method according to claim 1, wherein the organicfiller is a spherical or irregular shaped powder selected from the groupconsisting of unsaturated polyester, phenol resin, guanamine resin,melamine resin, polyetheretherketone, polysulfone, polyethersulfone andpolyimide resin.
 4. The method according to claim 1, comprising formingnozzle holes of the nozzle chamber plate and then molding integrallywith the vibration plate.
 5. The method according to claim 1, whereinthe thermosetting resin is an epoxy resin and the organic filler havinga particle size of 10 μm or less is a guanamine resin.
 6. The methodaccording to claim 5, wherein the epoxy resin is a phenol novolak basedepoxy resin.